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37 Cards in this Set

  • Front
  • Back
Population genetics provides a foundation for studying evolution:
The Modern Synthesis
The modern synthesis integrates Mendelian genetics with the Darwinian theory of evolution by natural selection and focuses on populations as the basic unit of evolution.
Gene Pools and Allele Frequencies
A population, a localized group of organisms that all belong to the same species, is united by its gene pool, the aggregate of all alleles in the pooulation.
The Hardy-Weinberg Theorem:
The Hardy-Weinberg theorem states that the frequencies of alleles and genotypes in a population will remain constant if Mendelian segregation and random mating are the only processes that affect the gene pool.
If p and q represent the relative frequencies of the only two possible alleles at a particular locus, the p^2 + 2pq + q^2 = 1, where p2 and q2 are the frequencies of the homozygous genotypes and 2pg is the frequency of tghe heterozygous genotype. Although many populations approximate HW equilibrium, the equilibrium in its strictest sense applies only if the population is large, mating at random, mutation is negligible, there is no gene flow from other populations, and all individuals have equal reproductive success.
Mutation and sexual recombination produce the variation that makes evolution possible:
New genes and new alleles originate only by mutation. Most mutations have no effect or are harmful, but a few increase adaptation.
Sexual Recombination
Genetic recombination between sexually reproducing organisms produces most of the variation in traits that makes adaptation possible.
Natural selection, genetic drift, and gene flow can alter a population's genetic composition:
Natural Selection
Differential success in reproduction results in certain alleles being passed to the next generation in greater proportions than others.
Genetic Drift
Chance fluctuations in allele frequencies from generation to generation tend to reduce genetic variation in populations.
Gene Flow
Genetic Exchange between populations tends to reduce differences between populations over time.
Natural Selection is the primary mechanism of adaptive evolution:
GEnetic Variation
Genetic variation includes variation among individuals within a population in discrete and quantitative characters, as well as geopraphic variation between populations.
A closer look at Natural Selection: One organism has a greater relative fitness than another if it leaves more descendants. Selection favors certain genotypes in a population by acting on the phenotypes of individual organims.
Natural seletion can favor relatively rare individuals at one end of the phenotypic range ( directional selection), can favor individuals at both extremes of the range rather than intermediate phenotypes (disruptive selection), or can act against extreme phenotypes (stabilizing selection).
The Preservation of GEnetic Variation
Diploidy maintains a reservoir of concealed recessive variation in heterozygotes. Balanced polymorphism may maintain variation at some gene loci as a result of heterozygote advantage or frequency-dependent selection.
Sexual Selection
Sexual selection leads to the evolution of secondary sex characteristics, which can give individuals an advantage in mating.
The Evolutionary Enigma of Sexual Reproduction
Enhanced disease resistance based on genetic variation is one possible explanation for the persistence of sexual reproduction despite its lesser reproductive output compared to asexual reproduction.
Why Natural Selection Cannot Fashion Perfect Organisms
Structures result from modified ancestral anatomy: adaptations are often compromises: the gene pool can be affected by genetic drift: and natural selction can act only on available variation.
The Biological Species Concept emphasizes reproductive isolation:
The biological species concept
A biological species is a group of populations whose individuals have the potential to interbreed and produce fertile offspring with each other but not with members of other species. The biological species concept emphasizes reproductive isolation through prezygotic and postzygotic barriers that can result in separating the gene pools of different populations.
Other Definitions of Species
Although particularly helpful in thinking about speciation processes, the biological species concept has some major limitations. For instance, it cannot be applied to organisms that are known only as fozzils or to organisms that reproduce only asexually. Thus, scientists maintain alternative species concepts, such as the morphological species concepts, that are useful in various contexts.
Speciation can take place with or without geogrepahic separation: Allopatric ("other country") Speciation
Allopatric speciation may occur when two populations of one species become geographically separated from each other. One or both populations may undergo evolutionary change during the period of separation. Should they come into contact pne more, they may be separated by the prezygotic and postzygotic isolating mechanisms that have accumulated.
Sympatric ("same country") Isolation:
A new species can originate while remaining in a geographically overla[ping area with the parent species. In particular, many plant species have evolved sympatrically throuigh polyploidy (multiplications of the chromosome number). Autopolyploids are species derived this way from one ancestral species.
Allopolyploids are species with multiple sets of chromosomes derived from different species with multiple sets of chromosomes derived from different species. Sympatric speciation can also result from the appearance of new ecological niches and from nonrandom mating in polymorphic populations.
Allopatric and Sympatric Speciation: A summary
In allopatric speciation, a new species forms while geopraphically isolated from its parent population. In sympatric speciation, a reproductive barrier isolates a subset of a population without geopraphic separation.
Adaptive Radiation
Adaptive radiation can occur when a poulation encounters a multiplicity of new or newly available ecological niches. This may happen during colonization of a new environment, such as newly formed volcanic islands, or after an environmental change that has resulted in mass extinctions of other species in an area.
Studying the Genetics of Speciation
The explosion of genomics is enabling researchers to identify specific genes involved in some cases of speciation.
The Tempo of Speciation
Eldredge and Gould's punctuated equilibrium model draws on fossil evidence showing that species change most as they arise from an ancestral species, after which they undergo relatively litle change for the rest of their existence. This model contrasts with a model of gradual change throughout a species' existence.
Macroevolutionary changes can accumulate through many speciation events:
Evolutionary Novelties
Most novel biological structures evolve in many stages from previously existing structures. Some complex structures, such as the eye, have had similar functions during all stages of their evolution. The most important functions of others, such as feathers, have changes.
Evolution of the Genes that Control Development
Many large evolutionary changes may have been associated with mutations in genes that regulate development. Such changes can affeect the timing of developmental events (heterochrony) or the spatial organization of body parts. Some of these changes result from mutational changes in homeotic genes and in the genes that regulate them.
Evolution is not Goal Oriented.
Long-term evolutionary trends may arise because of adaptation to a changing environment. In addition, according to the species selection model, trends may result when species with certain characteristics endure longer and speciate more often than those with other characteristics.
Ecology is the study of interactions between organisms and the environment:
Ecology and Evolutionary Biology
Events that occur in ecological time affect life on the scale of evolutionary time.
Organisms and the Environment:
Examples of questions that ecologists ask are, Who lives where? Why do they liver there? How many?
Ecologists use observations and experiments to test explanations for the distribution and abundance of species and other ecological phenomena. The environment of any organism includes both abiotic and biotic components.
Subfields of Ecology
Ecology can be divided into several subfields of study, ranging from the exology or organisms to the dynamics of ecosystems, landscapes, and the biosphere. Modern exological studies cross boundaries between traditionally separate areas.
Ecology and Environmental Issues
Ecology provides the scientific understanding underlying environmental issues. Many exologists favor the precautionary principle of "An ounce of prevention is worht a pound of cure."
Interactions between organisms and the environment limit the distribution of species:
Dispersal and Distribution
The dispersal of ogranisms results in broad patterns of geographical distribution. Natural range expansions and species transplants suggest hypotheses to explain why species are found where they are. Transplanted species may disrupt the ecosystem at the new site.
Behavior and Habitat Selection
Some organisms do not occupy all of their potentioal range. Species distribution may be limited by habitat selection behavior.
Biotic Factors
Biotic factors that affect the distribution of organisms include interactions with other species, such as predation and competition.
Abiotic Factors
Among important abiotic factors affecting species distribution are temperature, water, sunlight, wind, rocks, and soil.
Global climate patterns are largely determined by the input of solar energy and Earth's rotation around the sun. Regional, local, and seasonal effects on climate are influenced by bodies of water, mountains, and the changing angle of the sun over the year. Fine-scale differences in abiotic factors determine microclimates.
Abiotic and biotic factors influence the structure and drynamics of aquatic biomes
Aquatic biomes account for the largest part of the biosphere in terms of area and are generally stratified with regard to light penetration, temperature, and community structure. Marine biomes have a higher salt concentration than freshwater biomes.
Climate largely determines the distribution and structure of terrestrial biomes:
Climate and Terrestrial Biomes
Climographs show that temperature and precipitation are correlated with biomes, but because biomes overlap, other abiotic factors must play a role in biome location.
General Features of Terrestrial Biomes
Terrestrial biomes are often named for major physical or climatic factors and for their predominant vegetation. Stratification is an important feature of terrestrial biomes.